JP5256073B2 - Digital transmission system transmitter, receiver, and transmitter / receiver - Google Patents

Description

  The present invention relates to a technique for compensating for distortion generated in a satellite transmission line or the like, and more particularly to a digital transmission system transmission apparatus, reception apparatus, and transmission / reception apparatus.

  In the digital transmission system, a multi-level modulation system is often used so that more information can be transmitted in the frequency bandwidth available for each service. In order to increase the frequency utilization efficiency, it is necessary to increase the number of bits allocated per modulation signal symbol (the number of modulation levels), but the relationship between the upper limit of the information rate that can be transmitted per frequency 1 Hz and the signal-to-noise ratio is Limited by Shannon limit.

  As an example of a transmission form of information using a satellite transmission path, satellite digital broadcasting can be cited. For example, as illustrated in FIG. 9, the modulated wave signal from the transmission device 100 is transmitted to the reception device 200 via the satellite repeater 300. In such satellite digital broadcasting, the satellite repeater 300 mainly includes an input multiplexer (IMUX) filter, a traveling wave tube amplifier (TWTA), and an output multiplexer (OMUX) filter. The IMUX filter is used for each channel. Band extraction is performed, gain control is performed by TWTA, and unnecessary frequency components are suppressed by the OMUX filter.

  Thus, TWTA with high power efficiency is often used for the satellite repeater 300 due to hardware limitations. In order to make the most of the limited hardware of the satellite repeater 300, it is desirable to operate the TWTA in the saturation region so that the output of the satellite repeater 300 is maximized. However, since distortion generated in TWTA leads to transmission degradation, phase modulation is often used for transmission signals of transmission apparatus 100 and reception apparatus 200 as a modulation scheme that is resistant to transmission degradation caused by distortion generated in TWTA. .

  Currently, a transmission system called ISDB-S is used as a transmission system for satellite digital broadcasting in Japan, and phase modulation such as BPSK, QPSK, and 8PSK can be used. Moreover, in DVB-S2 which is a European transmission method, a modulation method called amplitude phase modulation (APSK), which further improves the frequency utilization efficiency, has been put into practical use. For example, if 16 APSK, the frequency utilization efficiency is 4 bps / Hz at the maximum, and if 32 APSK, the maximum 5 bps / Hz can be transmitted.

  In satellite digital broadcasting currently used, information correction is performed in a receiving apparatus using an error correction code. By adding a redundant signal called a parity bit to information to be sent, it is possible to control the redundancy (coding rate) of the signal and increase the resistance to noise. Error correction codes and modulation systems are closely related, and the relationship between frequency utilization efficiency and signal-to-noise ratio with redundancy added is defined by the Shannon limit. As one of powerful error correction codes having performance approaching the Shannon limit, an LDPC (Low Density Parity Check) code was proposed by Gallagher in 1962 (see, for example, Non-Patent Document 1).

  The LDPC code is a linear code defined by a very sparse check matrix H (the elements of the check matrix are 0 and 1 and the number of 1 is very small). The LDPC code is a powerful error correction code that can obtain transmission characteristics approaching the Shannon limit by increasing the code length and using an appropriate check matrix. DVB-S2 is a new European satellite broadcasting standard. The LDPC code is also adopted in the broadband wireless access standard IEEE 802.16e. By combining multi-level phase modulation and a powerful error correction code such as an LDPC code, transmission with higher frequency utilization efficiency has become possible.

R.G Gallager, “Low density parity check codes,” in Research Monograph series Cambridge, MIT Press, 1963

  In the prior art, assuming a IMUX filter, TWT, and OMUX filter that constitute a general satellite repeater 300, a repeater simulator in which the operating point of the TWT is set to OBO = 3.4 dB is reproduced by computer simulation, and will be described later. FIG. 16 shows an example of a signal obtained by adaptively equalizing a 32APSK modulated signal by a blind equalizer having a feedback FIR filter. FIG. 16A shows a constellation before applying blind equalization, and FIG. 16B shows a constellation after applying blind equalization. In the decision feedback FIR filter used to obtain FIG. 16, the step size is 2E-4, the feed forward filter tap length is 10, and the feedback filter tap length is 14. In addition, this blind algorithm uses a GCMCA algorithm (see the reference document described later).

  Referring to FIG. 16, it can be seen that the error vector magnitude is improved by performing blind equalization in the receiving apparatus, and the waveform quality is improved.

  However, in order to obtain the above performance in a transmission system that considers a satellite transmission path, it is necessary to mount an equalizer in all receiving apparatuses. This leads to an increase in the cost of the receiving apparatus, which is not preferable. In order to solve this problem in a transmission system that considers a satellite transmission path, highly reliable transmission path estimation information is acquired in advance on the transmission device side, and a transmission signal that reflects the transmission path characteristics is used. Therefore, it is desirable to transmit a signal having the same quality as when the receiving side equalizer is mounted without mounting the equalizer on all receiving apparatuses.

  SUMMARY OF THE INVENTION In view of the above-described problems, an object of the present invention is to provide a digital transmission system transmission device, reception device, and transmission / reception device that can improve transmission characteristics without increasing the cost of the reception device. .

  In the present invention, when adaptive equalization is performed for the purpose of compensating for distortion occurring in a transmission line, an adaptive equalizer is applied on both the transmission side and a specific reception side, and adaptive equalization is first performed on a specific reception side. After calculating the filter coefficient of the transmitter with high accuracy, this filter coefficient is applied to the adaptive equalizer on the transmission side, and the adaptive equalization that operates with the filter coefficient obtained on the specific reception side for the subsequent transmission signal By performing the processing, a transmission signal reflecting transmission path characteristics is generated. As a result, transmission of a transmission signal including the reverse characteristic of transmission path distortion is possible from the transmission side, and transmission performance can be improved. Preferably, the performance can be further improved by repeating the operation of applying the filter coefficient between the transmission and reception.

That is, the transmission apparatus of the present invention is configured to convert a digital transmission transmission signal in a digital transmission in which a plurality of reception apparatuses receive a signal transmitted from one transmission apparatus via a transmission path having common transmission path characteristics. A transmission device that performs adaptive equalization based on an error amount and transmits a modulated wave signal including an inverse characteristic of the transmission path, and transmits a modulation coefficient to the filter coefficient necessary for setting the adaptive equalization of the main signal when transmitting the modulated wave signal. A modulation signal generating means for generating a modulation wave signal of a main signal, having an initial operation mode for determining, and a steady operation mode for transmitting a modulation wave signal at a stationary time after determination of the filter coefficient, From the transmission side adaptive equalization means for performing adaptive equalization on the modulated wave signal of the main signal and a specific receiving device among the plurality of receiving devices, the main signal is converted into a complex error amount in an environment with good signal quality. Based on Receives the filter coefficients of 応等reduction and adaptive equalization that is generated, the setting of the filter coefficient of the transmission-side adaptive equalization means in accordance with said filter coefficients, transmission signal processed adaptive equalization of the transmission channel and a transmitting side filter coefficient update control means for controlling so inverse characteristic of the transmission path as a transmission signal is reflected before passing, the transmitting filter coefficient update control means, in the initial operation mode, the Until the filter coefficient generated by a specific receiving device is received, the adaptive equalization of the transmission side adaptive equalization means is controlled to output the modulated wave signal output from the modulation signal generation means to the outside, The filter coefficient for adaptive equalization of the transmission side adaptive equalization means is set with the filter coefficient finally determined for the filter coefficient generated on the receiving side in the steady operation mode.

  In the transmission apparatus of the present invention, the filter coefficient set for adaptive equalization by the transmission side adaptive equalization means has the same filter length as the filter coefficient used for adaptive equalization on the reception side. And

  In the transmission apparatus of the present invention, the transmission-side filter coefficient update control unit repeats reception of the reception-side filter coefficient a plurality of times in the initial operation mode, and the number of repetitions exceeds a preset value. Whether or not the filter coefficient is finally determined is determined depending on whether or not.

  In the transmission apparatus of the present invention, the filter coefficient is a value determined under a situation where a reception C / N equivalent value defined on the reception side is equal to or greater than a predetermined threshold value.

  In the transmission apparatus of the present invention, the transmission side adaptive equalization means is a feedback type adaptive equalizer used in combination with an LDPC code.

Furthermore, the receiving apparatus of the present invention is configured to convert a transmission signal of digital transmission into a complex error in digital transmission in which a plurality of receiving apparatuses receive a signal transmitted from one transmitting apparatus via a transmission path having common transmission path characteristics. a specific receiving device for transmitting a modulated wave signal and adaptive equalization based on the amount, upon transmission of a modulated wave signal, and the initial operation mode for determining the filter coefficients needed to configure the adaptive equalization of the main signal , Having a steady operation mode for transmitting a modulated wave signal in a stationary state after the filter coefficient is determined, and quadrature detecting means for quadrature detecting the modulated wave signal of digital transmission, and receiving C for the main signal subjected to quadrature detection A reception C / N determination means for determining / N and generating a reception C / N equivalent value and an adaptive equalization based on a complex error amount with respect to a main signal subjected to quadrature detection that operates in an environment with good signal quality. Receiving side And応等means, to generate a filter coefficient update control signal for controlling the continuation and stopping of the filter coefficient update using the received C / N value corresponding filter coefficient of the adaptive equalization of the reception side adaptive equalization means Receiving-side filter coefficient update control means for controlling the setting, and in the initial operation mode, the receiving-side filter coefficient update control means transmits the filter coefficient set for adaptive equalization by the receiving-side adaptive equalization means have a means for transmitting to the side, in the normal operating mode, and wherein receiving a transmission signal inverse characteristic of the transmission path is reflected before passing through the transmission path is processed adaptive equalization on the transmission side To do.

  In the receiving apparatus of the present invention, the filter coefficient set for adaptive equalization by the reception-side adaptive equalization means has the same filter length as the filter coefficient used for adaptive equalization on the transmission side. And

  In the receiving apparatus of the present invention, the reception-side filter coefficient update control means sends the filter coefficient set to the adaptive equalization of the reception-side adaptive equalization means to the transmission side a plurality of times in the initial operation mode. It is characterized by repeating transmission.

  In the receiving apparatus of the present invention, the receiving-side filter coefficient update control means can output the filter coefficient of the receiving-side adaptive filter that operates in a situation where the specified received C / N equivalent value is equal to or greater than a predetermined threshold value. A control signal for determining the filter coefficient is sent to the reception-side adaptive equalization means.

  In the receiving apparatus of the present invention, the receiving side adaptive equalization means is a feedback type adaptive equalizer used in combination with an LDPC code.

  Moreover, this invention can also be comprised as a transmission / reception apparatus provided with the transmission apparatus of this invention, and the reception apparatus of this invention.

  According to the present invention, it is possible to realize a digital transmission transmission device, a reception device, and a transmission / reception device that can improve transmission characteristics without increasing the cost of the reception device.

It is a figure which shows schematic structure of the advanced satellite broadcasting system of one Example by this invention. It is a figure which shows the structural example of the transmitter of one Example by this invention. It is a figure which shows the LDPC decoding part in the receiver of one Example by this invention. It is a figure which shows the structural example of the adaptive equalizer (decision feedback type FIR filter) with which the transmitter of one Example by this invention is provided. It is a figure which shows the structural example of the adaptive equalizer (decision feedback type FIR filter) with which the receiver of one Example by this invention is provided. It is a flowchart explaining operation | movement of the transmitter of one Example by this invention, and a receiver. It is a figure which shows the constellation of the 32APSK transmission signal in the transmitter of one Example by this invention, and a receiver. It is a figure which shows the computer simulation result of the 32APSK coding rate 4/5 C / N versus bit error rate characteristic obtained with the transmitter and receiver of one Example by this invention. It is a figure which shows an example of the transmission form of the information using the conventional satellite transmission path. It is a figure which shows the structure of the transmission apparatus of the conventional advanced satellite broadcast system. It is a block diagram which shows schematic structure of the receiver of the conventional advanced satellite broadcast system. It is a figure which shows the example of the modulation wave signal format of an advanced satellite broadcast system. It is a figure which shows the example of one transmission form of a pilot signal. It is a figure which shows some LDPC decoding parts of the conventional receiver. It is a block diagram of a decision feedback type FIR filter. It is a figure which shows the example of a signal which adaptively equalized the 32APSK modulation signal by the blind equalizer which has a decision feedback type FIR filter.

  First, in order to facilitate understanding of the present invention, a schematic configuration of the transmitter 100 and the receiver 200 of the advanced satellite broadcasting system using the LDPC code will be briefly described. For simplification of description, only the portion according to the present invention will be described. However, the advanced satellite broadcasting transmission device 100 and the reception device 200 may replace the LDPC code with another correction code method or use it in combination. Furthermore, interleavers can be used in appropriate combinations.

  FIG. 10 is a diagram illustrating a configuration of a conventional advanced satellite broadcasting transmission device. The transmission apparatus 100 includes a frame generation unit 110, an LDPC encoding unit 120 (hereinafter also referred to as an encoder), an energy spreading unit 130, a mapping unit 140, and a time division multiplexing / orthogonal modulation unit 150. Prepare. That is, when transmitting a data stream, the transmission apparatus 100 performs a series of processes from generation of a signal of a multiplexed frame of a plurality of slots in FIG. 12 to be described later to generation of a modulated wave signal.

  The frame generation unit 110 functions together with the LDPC encoding unit 120 to generate an LDPC parity. Therefore, the frame generation unit 110 and the LDPC encoding unit 120 generate a frame of a plurality of slots in FIG. The multiplexed frame generated by the frame generation unit 110 is generated so that the number of slots, the amount of dummy, the slot length, the synchronization bit length, the pilot bit length, and the TMCC and parity bit lengths are predetermined numbers. The

  The LDPC encoding unit 120 performs LDPC encoding with a predetermined period on the data and the transmission control signal. The specific method of LDPC encoding is known and is not the subject of this application and will not be described further.

  The energy spreading unit 130 inputs a predetermined number of slots of each multiplex frame, and performs energy spreading (bit randomization) on the entire data.

  The bit randomized signal from the energy spreading unit 130 is switched according to various modulation schemes (BPSK, APSK, etc.) while inserting synchronization and pilot signals as appropriate, and a mapping unit 140 (a plurality of mappings corresponding to the modulation schemes). ).

  The mapping unit 140 performs mapping according to the modulation scheme specified by TMCC synchronization.

  The time division multiplexing / orthogonal modulation unit 150 performs time division multiplexing in units of frames, performs orthogonal modulation, and generates a modulated wave signal.

  FIG. 11 is a block diagram showing a schematic configuration of a conventional advanced satellite broadcasting receiver 200. The receiving apparatus 200 includes a channel selection unit 210, an orthogonal detection unit 220, a transmission control signal decoding unit 230, an energy despreading unit 240, and an LDPC decoding unit 250.

  The channel selection unit 210 receives the modulated wave signal from the transmission apparatus 100, selects a channel of a predetermined frequency band, and converts the signal of the channel into a signal of a predetermined frequency handled by the quadrature detection unit 220. For example, if the modulated wave signal is a satellite broadcast wave, a 12 GHz band broadcast wave (modulated wave signal) is received by a BS antenna, and a 1 GHz band BS-IF signal is transmitted using a known frequency converter (not shown). Convert to

  The quadrature detection unit 220 receives a signal (for example, a BS-IF signal) of a predetermined frequency of the channel selected by the channel selection unit 210 and converts it into a synchronous baseband signal.

  The transmission control signal decoding unit 230 receives the synchronous baseband signal converted by the quadrature detection unit 220, first detects a synchronous byte of the TMCC signal, and uses this as a reference to periodically BPSK modulated waves. The position of a certain phase reference burst signal is also detected. Also, TMCC information decoding processing for modulation scheme and error correction information transmitted by the TMCC signal is performed through the energy despreading unit 240. Transmission control information (modulation scheme / error correction TMCC information) decoded by transmission control signal decoding section 230 is input to LDPC decoding section 250.

  The energy despreading unit 240 performs the energy despreading process by adding the same pseudorandom code again by MOD2 in order to restore the process in which the pseudorandom code is added by MOD2 in the energy spreading unit 130 of the transmission apparatus 100.

  The LDPC decoding unit 250 receives the synchronous baseband signal from the quadrature detection unit 220 and also receives the modulation scheme / error correction information detected by the transmission control signal decoding unit 230, and converts the synchronous baseband signal into the LDPC code. The decoding process is performed using the parity check matrix.

  As described above, the advanced satellite broadcasting transmission device 100 and the reception device 200 using the LDPC code can be combined with multi-level phase modulation and a powerful error correction code such as an LDPC code to achieve higher frequency utilization efficiency. Can be transmitted.

  However, although such a strong error correction code such as an LDPC code has an excellent correction capability for white noise, the correction capability for signal deterioration against distortion inherent in a satellite transmission path is not sufficient. In particular, when amplitude phase modulation such as 16APSK or 32APSK is used for a satellite transmission path, signal deterioration due to waveform distortion generated in an amplifier such as TWTA used in the satellite repeater 300 or the earth station is more serious than phase modulation.

  In general, as a method of suppressing waveform distortion generated in an amplifier, a technique of operating the amplifier in a more linear region by lowering the output level from the saturation region is used. However, in this case, transmission degradation due to distortion is reduced, but the output of the satellite repeater 300 is reduced, leading to a reduction in received signals on the ground. Therefore, in order to apply APSK in satellite broadcasting or the like, it is essential to use a transmission method that is resistant to transmission deterioration due to distortion without reducing satellite output as much as possible.

  In the latest satellite digital broadcasting systems such as DVB-S2, a technique (maximum likelihood decoding) for maximizing the posterior probability based on Bayesian theory is used as a decoding method for error correction codes. The posterior probability is obtained by a likelihood function (formula (1)).

  From the definition of the likelihood function, the likelihood function and the Euclidean distance indicating the distance between the received signal and the ideal signal point are closely related. In a transmission path containing only white noise, the received signal point generates a random deviation of a Gaussian distribution according to S / N. In a transmission path including specific distortion other than white noise, Signal point transition with amplitude and phase deviation occurs. In particular, when APSK is input to the non-linear amplifier, the signal points belonging to the concentric circle having the largest amplitude cause a larger signal deviation because of the convenience of transmitting the APSK by combining a plurality of types of concentric circles.

  In addition, http: // www. soumu. go. jp / joho_tsusin / policyreports / joho_tsusin / bunkakai / 080729_1. In response to Advisory No. 2023 “Technical Conditions for Broadcasting Systems” from the Minister of Internal Affairs and Communications, published as “Document 60-1-2 Broadcasting System Committee Report” to html, In the Advanced Satellite Digital Broadcasting System (hereinafter referred to as Advanced Satellite Broadcasting System) shown in the report “Report of the Information and Communications Council Information and Communication Technology Subcommittee Broadcasting System Committee Report” (July 29, 2008), APSK Consideration is also given to the improvement of transmission characteristics.

  FIG. 12 shows an example of a modulated wave signal format of the advanced satellite broadcasting system. The modulation wave signal can be changed in transmission parameters including a modulation method and an error correction code coding rate in units of frames. One frame is composed of 120 modulation slots, and can be transmitted by specifying a modulation method and a coding rate for every five modulation slots. In each modulation slot, a 24-symbol synchronization signal, a 32-symbol pilot signal, and a pair of 136-symbol data and a 4-symbol TMCC signal are time-division multiplexed 66 times.

  FIG. 13 is an example of a transmission form of a pilot signal, and shows a correspondence diagram of known transmission bits with respect to transmission symbols whose transmission order is determined in advance. As shown in FIG. 13, in the case of 32APSK, signal points corresponding to symbols “00000” to “11111” are sequentially transmitted as pilot signals. In FIG. 13A, FIG. 13B, and FIG. 13C, signal points corresponding to the first symbol, the second symbol, and the 32nd symbol are represented by “black circles”, respectively.

  FIG. 14 shows a part of an LDPC decoding unit 250 of a conventionally known receiving apparatus 200 using this pilot signal. In the case of a system that does not include a pilot signal, LDPC decoding is performed on the I and Q signals subjected to quadrature detection while referring to a likelihood table. The LDPC decoding unit 250 averages the pilot signal for each symbol. To obtain the signal point constellation after being affected by nonlinear distortion in the transmission path, and to generate or update the likelihood table based on the obtained signal point constellation, the performance can be improved (same as above). (Refer to Reference Material 1-8 “Improvement of reception characteristics by pilot signal”).

  Specifically, the LDPC decoding unit 250 includes a pilot signal extraction unit 252, a pilot signal averaging processing unit 253, a likelihood table generation unit 254, and a likelihood stored in a predetermined memory (not shown). A table 255 and an LDPC decoder 251 are provided.

  The pilot signal extraction unit 252 inputs the synchronous baseband signal converted by the quadrature detection unit 220, and uses the signal of the synchronization information (pilot timing signal) indicating the pilot timing in the TMCC signal detected in advance, to generate the pilot signal. The position of the signal point is extracted and sequentially transmitted to the pilot signal averaging processing unit 253.

  Pilot signal averaging processing section 253 averages pilot signal signal points for each symbol, and sends this information to likelihood table generation section 254.

  The likelihood table generation unit 254 represents a decoder output log likelihood ratio (LLR) for the signal points of the pilot signal averaged for each symbol, and is used for likelihood calculation in LDPC decoding. 255 is generated and stored in a predetermined memory or updated. The likelihood table 255 is preferably generated individually according to the modulation scheme and coding rate with a predetermined slot length, and information on the modulation scheme and coding rate used to generate the likelihood table 255. Is obtained from a signal (referred to as a modulation scheme / coding rate selection signal) according to TMCC information in the TMCC signal detected in advance.

  Based on the LLR of the likelihood table 255 and the modulation scheme / coding rate selection signal, the LDPC decoder 251 performs LDPC decoding on the information of the synchronous baseband signal converted by the quadrature detection unit 220 and transmits a decoded signal. .

  If such a fixed known pattern (for example, a repeated pattern of pilot signal points) is periodically multiplexed, a line spectrum is generated in the frequency component of the modulation signal. Spread energy on the transmitting side.

  Here, use of an adaptive equalizer can be cited as a method for compensating for transmission path distortion in the conventional receiving apparatus 200. As one form of the adaptive equalizer, the influence of transmission path distortion can be reduced only from a received signal. Possible blind equalizers are often used (for example, reference: Kil Nam OH, “A Single / Multilevel Modulus Algorithm for Blind Equalization of QAM Signals” IEICE TRANS. FUNDAMENTALS. VOL.E80-A, N.6. 1997 (See June)

  The blind equalizer used on the receiving side is a kind of adaptive filter provided in the preceding stage of the LDPC decoder 251, and by appropriately selecting the filter tap length, step size, and error vector calculation method, This is an adaptive equalizer capable of reducing the generated distortion and changing the reception signal point to a symbol point close to the transmission signal. The blind equalizer can be verified using the decision feedback FIR filter 256 shown in FIG. The step size s is 2E-4, the tap length M of the feed forward filter (FF) 2561 is 10, the tap length L of the feedback filter (FB) 2564 is 14, and the blind algorithm uses the GCMCA algorithm (see the above reference) ).

  Specifically, the decision feedback type FIR filter 256 includes a feedforward filter (FF) 2561, an equalizer output unit 2562, a determination unit 2563, a feedback filter (FB) 2564, an adder 2565, and a filter coefficient. And an update unit 2566.

The feedforward filter (FF) 2561 has filter coefficients W _FF : [W ₀ , W ₁ ,..., W _M ] corresponding to the tap length M, and inputs the input signal vector x (n). Vector sequence x _FF : [x (n), x (n−1),..., X (n−M)] ^T is held, and the product sum of the feedforward filter coefficient W _FF and the input vector sequence X _FF Perform the operation. Here, T represents transposition of the matrix.

The feedback filter (FB) 2564 has filter coefficients W _FB : [W _{M + 1} , W _{M + 2} ,..., W _{M + L} ] corresponding to the tap length L, and a determiner output d (n) of the determination unit 2563 described later. respect, the determination output sequence _{d FB: [d (n-} 1), d (n-2), ···, d (n-L)] holding the ^T, the feedback filter coefficient W _FB and judgment output Perform product-sum operation with column d _FB .

  The adder 2565 outputs a value obtained by subtracting the output 2564a of the feedback filter (FB) 2564 from the output of the feedforward filter (FF) 2561 to the equalizer output unit 2562.

  The determination unit 2563 determines the minimum Euclidean distance from the ideal symbol point determined by a known modulation scheme for the equalizer output z (n) obtained by the equalizer output unit 2562, and the minimum Euclidean distance is obtained. The ideal symbol point is output to the feedback filter (FB) 2564 as the determiner output d (n). At the same time, the filter output d (n) is output to the filter coefficient update unit 2566 for updating the filter coefficient.

  The equalizer output unit 2562 sends out the signal 2562b of the equalizer output z (n) obtained from the adder 2565.

z (n) = x ′ (n) ^T · W (n) (2)
Where x ′ (n) = [x (n), x (n−1),..., X (n−M),
d (n-1), d (n-2), ..., d (n-L)]

The filter coefficient update unit 2566 obtains an error vector e (n) from the equalizer output z (n) and the determiner output d (n), and feedforwards it with the LMS algorithm using e (n) and the step size s. The filter (FF) coefficient W _FF and the feedback filter (FB) coefficient W _FB are sequentially updated. (See references above).

  However, it is not preferable to install such a blind equalizer in all receiving apparatuses because it increases the cost of the receiving apparatus. Therefore, according to the present invention, the transmission device 10 has a blind equalizer by acquiring the adaptive equalization filter coefficient used in the specific reception device 20 via the satellite repeater 300, for example. This makes it possible to transmit a good main signal even to a receiver that is not present.

  Hereinafter, a transmitting apparatus and a receiving apparatus according to an embodiment of the present invention will be described.

  FIG. 1 is a diagram showing a schematic configuration of an advanced satellite broadcasting system according to an embodiment of the present invention. FIG. 2 is a diagram illustrating a configuration example of a transmission apparatus according to an embodiment of the present invention. The configuration of the receiving apparatus according to an embodiment of the present invention can use the configuration example shown in FIG. 11, but has the LDPC decoding unit 50 shown in FIG. 3, unlike the configuration shown in FIG. 14. FIG. 4 is a diagram illustrating a configuration example of an adaptive equalizer included in the transmission apparatus according to an embodiment of the present invention. FIG. 5 illustrates an adaptive equalizer included in the reception apparatus according to the embodiment of the present invention. It is a figure which shows the example of a structure.

  Referring to FIG. 1, modulated wave signals from the transmitter 10 are received by receivers 200-1, 200-2,..., 200-N via the satellite repeater 300 (N is a natural number of 1 or more, respectively). , Which corresponds to the receiving apparatus shown in FIG. 11 and FIG. 14), is transmitted to the receiving apparatus 20 of the present embodiment via the satellite repeater 300. In such satellite digital broadcasting, the satellite repeater 300 mainly includes an input multiplexer (IMUX) filter, a traveling wave tube amplifier (TWTA), and an output multiplexer (OMUX) filter. With the gain control by TWTA, Intended for conditions that may cause waveform distortion.

  The receiving apparatus 20 performs reception C / N determination of the main signal from the transmitting apparatus 10 via the satellite repeater 300, calculates a filter coefficient effective for adaptive equalization, and directly connects the information of this filter coefficient to (Or via, for example, an earth station (such as a terrestrial repeater)). By repeating this series of operations one or more times, the transmission device 10 can transmit a modulated wave signal that has been subjected to distortion compensation of the transmission signal via the satellite repeater 300 in advance. The modulated wave signal subjected to distortion compensation in advance is a good modulated wave signal regardless of whether or not the receiving devices 200-1, 200-2,..., 200-N have an adaptive equalizer. Can be received.

  More specifically, one feature of an adaptive equalizer such as a blind equalizer will be described. The filter coefficient of the adaptive equalizer corresponds to the inverse characteristic of the impulse response of the transmission path. That is, when the reception-side adaptive equalizer 51 operates stably (that is, when adaptive equalization is performed), the reception-side adaptive equalizer 51 operates to bring the distorted signal closer to an ideal signal. As a result, the inverse characteristic of the impulse response of the transmission path can be obtained from the filter coefficient of the receiving side adaptive equalizer 51.

  Therefore, in order to reflect the channel estimation information in the transmission signal on the transmission side using this feature, the reception side filter coefficient obtained by the stably operated reception side adaptive equalizer 51 is reflected in the transmission signal in the transmission device 10. I will let you. Specifically, a transmission side adaptive equalizer 13 having the same filter length as that of the reception side adaptive equalizer 51 is also prepared in the transmission device 10. First, as an initial state of the transmission side adaptive equalizer 13, transmission is performed. Only the median value of the side filter coefficients is fixed to 1 and all others are fixed to 0, that is, the transmission signal generated by the advanced BS modulation signal generation unit 11 is transmitted as it is without operating the transmission side adaptive equalizer 13 To do.

  Subsequently, in a state where the transmission apparatus 10 maintains this initial state, the reception apparatus 20 detects and receives a signal that has passed through a transmission path such as the satellite repeater 300 by the quadrature detection unit 220. Subsequently, the reception apparatus 20 operates the reception-side adaptive equalizer 51 in an environment with good signal quality (for example, in the case of a satellite transmission path, an environment with high reception C / N such as when the sky is clear). Further, based on the reception C / N information obtained by the reception C / N determination unit 52, the reception-side filter coefficient set in the reception-side filter coefficient update control unit 53 is monitored or updated, so that the reception-side adaptation, etc. It is possible to obtain the reception-side filter coefficient under the condition that the quantizer 51 has reached a stable operation. The reception-side filter coefficient obtained here corresponds to the inverse characteristic of the impulse response of the transmission path through which the transmission signal has passed.

  Next, the reception side filter coefficient is applied to the filter coefficient of the transmission side adaptive equalizer 13 to operate the transmission side adaptive equalizer 13. Since the reception-side filter coefficient has information reflecting the reverse characteristic of the transmission path, the transmission signal adaptively equalized using the reception-side filter coefficient for the ideal transmission signal on the transmission side passes through the transmission path. The transmission signal reflects the reverse characteristics of the transmission path before. Therefore, when a transmission signal that reflects the reverse characteristics of this transmission path passes through the same transmission path, the received signal is a signal with a reduced influence of distortion because the effect is to cancel the transmission path distortion. It becomes.

  Therefore, transmission signals reflecting the reverse characteristics of the transmission path can be transmitted all at once through the satellite transmission path, and all the receivers 20, 200-1, 200 receive the signals in which distortion caused by the transmission path is canceled. -2, ..., 200-N can be received simultaneously. The reception-side adaptive equalizer 51 can be configured only as necessary for adaptive equalization of the transmission point for changing the transmission signal, and all other reception apparatuses 20, 200-1, 200- 2,..., 200-N do not need to have an adaptive equalizer in particular, or even when having an adaptive equalizer, it is possible to improve reception performance without changing the filter coefficient. Become. Furthermore, the update of the filter coefficients of the adaptive equalizers 13 and 51 between transmission and reception can be repeatedly performed via the transmission side filter coefficient update control unit 12 and the reception side filter coefficient update control unit 53, respectively. Can further improve the transmission performance. Therefore, from the viewpoint of improving transmission performance, it is preferable that the transmission side and reception side adaptive equalizers be feedback adaptive equalizers used in combination with LDPC codes.

  Hereinafter, the transmission device 10 and the reception device 20 of the present embodiment will be described in more detail.

  Referring to FIG. 2, the transmission apparatus 10 includes an advanced BS modulation signal generation unit 11, a transmission side filter coefficient update control unit 12, and a transmission side adaptive equalizer 13. The advanced BS modulation signal generation unit 11 includes a frame generation unit 110, an LDPC encoding unit 120, an energy spreading unit 130, a mapping unit 140, and a time division multiplexing / orthogonal modulation unit 150. That is, the transmission apparatus 10 includes an advanced BS modulation signal generation unit 11 equivalent to the function of the transmission apparatus 100 illustrated in FIG. 10, but the transmission apparatus 100 includes a transmission-side adaptive equalizer 13 and a transmission-side filter coefficient update. It differs in that it further comprises a control unit 12. Therefore, the description of the advanced BS modulation signal generation unit 11 is the same as that of the transmission apparatus 100 shown in FIG. 10, and further description is omitted.

  The transmission-side filter coefficient update control unit 12 functions to receive the filter coefficient generated on the reception side and control the setting of the filter coefficient for transmission-side adaptive equalization, and transmit the modulated wave signal. At this time, it has a function of performing different control in two types of an initial operation mode and a steady operation mode. The initial operation mode is an operation mode for determining the filter coefficient necessary for setting the adaptive equalization of the main signal when transmitting the modulated wave signal. The steady operation mode is determined after the filter coefficient for adaptive equalization is determined. This is an operation mode for transmitting a regular modulated wave signal. In other words, the transmission-side filter coefficient update control unit 12 externally transmits the modulated wave signal output from the advanced BS modulation signal generation unit 11 until reception with the filter coefficient generated on the reception device 20 side in the initial operation mode. The adaptive equalization of the transmission side adaptive equalizer 13 is controlled so as to output, and the filter coefficient of the transmission side adaptive equalizer 13 is finally determined with the filter coefficient finally determined for the filter coefficient generated on the reception device 20 side in the steady operation mode. Sets filter coefficients for adaptive equalization. Further, in the initial stage in the initial operation mode, the transmission-side filter coefficient update control unit 12 fixes only the median value of the transmission-side filter coefficients of the transmission adaptive equalizer 13 to 1 and all others to 0. Then, the transmission adaptive equalizer 13 is operated. That is, in the initial stage in the initial operation mode, the transmission side adaptive equalizer 13 does not operate as an equalizer, and the transmission side adaptive equalizer 13 directly uses the transmission signal output from the advanced BS modulation signal generation unit 11. Output as a modulated wave signal.

  Further, in the second stage in the initial operation mode, the transmission side filter coefficient update control unit 12 can repeat the determination operation of the filter coefficient for use in the steady operation mode, and the reception side filter coefficient obtained from the reception device 20 again. And the reception side filter coefficient can be set in the transmission adaptive equalizer 13 as the transmission side filter coefficient of the transmission adaptive equalizer 13. That is, in the second stage in the initial operation mode, the transmission side adaptive equalizer 13 operates as an equalizer, and the transmission side adaptive equalizer 13 transmits the transmission output from the advanced BS modulation signal generation unit 11. A modulated wave signal adaptively equalized using the reception-side filter coefficient is output for the signal.

  Further, the transmission-side filter coefficient update control unit 12 continuously receives the reception-side filter coefficient obtained from the reception device 10 and uses this reception-side filter coefficient as the transmission-side filter coefficient of the transmission adaptive equalizer 13 for transmission. It can also be set in the adaptive equalizer 13. Therefore, when the transmission / reception equalization repetition number P defined as a common parameter for transmission / reception equalization processing between the transmission / reception units is set, the transmission-side filter coefficient update control unit 12 is set to a predetermined set in the P-stage in the initial operation mode. It is possible to repeatedly set or change the filter coefficient up to the transmission / reception equalization repetition target number G. For example, the transmission side filter coefficient update control unit 12 receives the filter coefficient generated on the receiving device 20 side multiple times in the initial operation mode, and whether or not the number of repetitions exceeds a preset value, The filter coefficient used in the steady operation mode can be finally determined. On the receiving device 20 side, when determining a filter coefficient to be used between transmission and reception in the initial operation mode, a filter coefficient is obtained when the reception-side adaptive filter operates in a situation where the specified reception C / N equivalent value is equal to or greater than a predetermined threshold. To be determined.

  The transmission-side adaptive equalizer 13 is an equalizer that functions as a decision feedback FIR filter shown in FIG. 4, and performs transmission-side filter coefficient update control on the transmission signal output from the advanced BS modulation signal generation unit 11. Adaptive equalization is performed according to the filter coefficient controlled by the unit 12, and the modulated wave signal subjected to the adaptive equalization is transmitted to the outside. It is preferable that the filter coefficient set for adaptive equalization of the transmission side adaptive equalizer 13 has the same filter length as the adaptive equalization filter coefficient used on the receiving apparatus 20 side.

  Referring to FIG. 3, there is shown a schematic configuration of the LDPC decoding unit 50 in the receiving device 20 of the present embodiment of the advanced satellite broadcasting system.

  The LDPC decoding unit 50 according to the present embodiment includes a pilot signal extraction unit 252, a pilot signal averaging processing unit 253, a likelihood table list generation unit 254, and a likelihood stored in a predetermined memory (not shown). A table 255, an LDPC decoder 251, a reception-side adaptive equalizer 51, a reception C / N determination unit 52, and a reception-side filter coefficient update control unit 53 are provided. The pilot signal extraction unit 252, the pilot signal averaging processing unit 253, the likelihood table list generation unit 254, the likelihood table 255, and the LDPC decoder 251 in the LDPC decoding unit 50 of the present embodiment are respectively shown in FIG. 14 has the same functions as those shown in FIG. Therefore, the LDPC decoding unit 50 of the present embodiment further includes a reception-side adaptive equalizer 51, a reception C / N determination unit 52, and a reception-side filter coefficient update control unit 53, so that the LDPC shown in FIG. This is different from the decoding unit 250. Therefore, the reception side adaptive equalizer 51, the reception C / N determination unit 52, and the reception side filter coefficient update control unit 53 will be described in detail.

  The reception-side adaptive equalizer 51 is an equalizer that functions as a decision feedback FIR filter shown in FIG. 5, and an I signal and a Q signal (received IQ signal) obtained from the quadrature detection unit 220 through the energy despreading unit 240. The output subjected to adaptive equalization is sent to the LDPC decoder 51.

  The reception C / N determination unit 52 determines the reception C / N of the pilot signal using the modulation error ratio (MER) or the like from the reception IQ signal, and an arbitrarily determined value corresponding to the reception C / N ( (Receive C / N equivalent value) is sent to the reception-side filter coefficient update control unit 53.

  The reception-side filter coefficient update control unit 53 inputs the reception C / N equivalent value evaluated by the reception C / N determination unit 52, and satisfies a predetermined value (for example, 20 dB or more) of the reception C / N. A filter coefficient update control signal for controlling the continuation and stop of coefficient update is generated so as to obtain a filter coefficient when the reception-side adaptive equalizer 51 is operated, and is transmitted to the reception-side adaptive equalizer 51. The filter coefficient set in the receiving side adaptive equalizer 51 is transmitted to the transmitting apparatus 10 as information on the receiving side filter coefficient during the initial operation mode.

  FIG. 4 shows a configuration example of an adaptive filter corresponding to the transmission side adaptive equalizer 13 in the transmission apparatus 10. This adaptive filter can be configured as a blind equalizer as shown in FIG. 4. By appropriately selecting the filter tap length, step size, and error vector calculation method, distortion generated in the transmission path can be reduced. It is possible to reduce and change the reception signal point to a symbol point close to the transmission signal. 4 includes a feedforward filter (FF) 131, an equalizer output unit 132, a determination unit 133, a feedback filter (FB) 134, and an addition. Unit 135 and a filter coefficient updating unit 136, each of which is a feed-forward filter (FF) 2561 in the decision feedback FIR filter described above with reference to FIG. 15, an equalizer output unit 2562, a determination unit 2563, It has functions corresponding to a feedback filter (FB) 2564, an adder 2565, and a filter coefficient updater 2566. The filter coefficient updating unit 136 converts the filter coefficient obtained from the transmission-side filter coefficient update control unit 12 (for example, the reception-side filter coefficient obtained by the receiving device 10) into a feedforward filter (FF) 131 and a feedback filter (FB) 134. It works by setting to.

  FIG. 5 shows a configuration example of an adaptive filter corresponding to the reception-side adaptive equalizer 51 in the reception device 20. This adaptive filter can be configured as a blind equalizer as shown in FIG. 5, and by appropriately selecting the filter tap length, step size, and error vector calculation method, distortion generated in the transmission path can be reduced. It is possible to reduce and change the reception signal point to a symbol point close to the transmission signal. The blind equalizer (decision feedback type FIR filter) shown in FIG. 5 includes a feedforward filter (FF) 511, an equalizer output unit 512, a determination unit 513, a feedback filter (FB) 514, and an addition Unit 515 and a filter coefficient updating unit 516, each of which is a feedforward filter (FF) 131 in the decision feedback FIR filter described above with reference to FIG. 4, an equalizer output unit 132, a determination unit 133, It has functions corresponding to the feedback filter (FB) 134, the adding unit 135, and the filter coefficient updating unit 136. The filter coefficient update unit 516 receives the filter coefficient update control information obtained from the reception-side filter coefficient update control unit 53, and receives the filter coefficient update control information based on the received C / N equivalent value evaluated by the reception C / N determination unit 52. Receiving side filter coefficients (feed forward filter (FF) 511 and feedback filter (FB) 514) when the receiving side adaptive equalizer 51 is operated under a condition satisfying a predetermined value of C / N (for example, 20 dB or more). Is transmitted to the transmission device 10 via the reception-side filter coefficient update control unit 53 as a reception-side filter coefficient. On the other hand, when updating the filter coefficient between repeated transmission and reception in the initial operation mode, the filter coefficient update unit 516 uses the filter coefficient obtained by the feed forward filter (FF) 511 and the feedback filter (FB) 514. It can transmit to the transmitter 10 as information of a receiving side filter coefficient.

  Next, operations of the transmission device and the reception device of the present embodiment will be described with reference to FIG.

  FIG. 6 is a flowchart for explaining the operation of the transmission apparatus and the reception apparatus of this embodiment. Here, as described above, all symbol sequences are assumed to be complex signals, and 32APSK will be described as an example. Further, the transmission device 10 and the reception device 20 of the present embodiment have a decision feedback type blind adaptive equalizer represented by the decision feedback type FIR filter shown in FIGS. 4 and 5 having the same filter length. Assuming that a signal is received via the satellite repeater 300 shown in FIG. 6, it is assumed that the transmission path distortion occurs only in the process from the transmission section to the reception apparatus via the transmission path.

  As illustrated in FIG. 1, the transmission device 10 and the reception device 20 can be configured to be connected to each other in order to transmit the filter coefficient from the reception device 20 to the transmission device 10. In consideration of a satellite transmission path (satellite repeater 200 or the like), both the transmission device 10 and the reception device 20 are the easiest configuration to be installed in the same place, but are not necessarily in the same place. When both are separated, an arbitrary communication path for transmitting the filter coefficient between transmission and reception may be ensured.

  Referring to FIG. 6, in step S <b> 1, the transmitting apparatus 10 causes the advanced BS modulation signal generation unit 11 to generate a 32APSK modulation signal that conforms to the advanced satellite digital broadcast transmission signal. In the subsequent steps, the description will be made assuming that the transmission signal to be transmitted is continuously transmitted without stopping regardless of the operation of the adaptive equalizer according to the present embodiment.

  Subsequently, in step S <b> 2, the transmission apparatus 10 receives the 32APSK modulation signal transmitted from the advanced BS modulation signal generation unit 11 and inputs the 32APSK modulation signal to the transmission side adaptive equalizer 13. In the initial stage of the initial operation mode of the transmission side adaptive equalizer 13 in step S2, only the median value of the transmission side filter coefficients of the transmission side adaptive equalizer 13 is fixed to 1, and all others are fixed to 0. Then, the transmission side adaptive equalizer 13 is operated. That is, in the initial stage of the initial operation mode, the transmission side adaptive equalizer 13 does not operate as an equalizer, and the transmission signal is output as it is from the transmission side adaptive equalizer 13. Here, for the convenience of the following description, as a common parameter for transmission / reception equalization processing between transmission / reception units, the number of repetitions of equalization operation between transmission / reception (referred to as transmission / reception equalization repetition number in this specification) P Define. That is, at the time of step S2, the transmission / reception equalization repetition number P is zero. In addition, a repetition target number of equalization operations between transmission and reception (referred to as transmission / reception equalization repetition target number in this specification) G is set. The transmission / reception equalization repetition number P and the transmission / reception number equalization repetition target number G are controlled by the transmission-side filter coefficient update control unit 12.

  Subsequently, in step S3, the output of the transmission side adaptive equalizer 13 is output to the transmission line as a transmission signal.

  Subsequently, in step S <b> 4, the reception apparatus 20 receives the signal that has passed through the transmission path by the quadrature detection unit 220, and evaluates the reception C / N by the reception C / N determination unit 52. The received signal is also input to the receiving side adaptive equalizer 51. A value corresponding to this reception C / N (referred to as a reception C / N equivalent value in this specification) can be constantly monitored and grasped by the reception device 20 using a modulation error ratio (MER) or the like. Is possible. The reception-side filter coefficient update control unit 53 receives the evaluated received C / N equivalent value and generates a filter coefficient update control signal for the reception-side adaptive equalizer 51. With this control signal, the reception-side adaptive equalizer 51 controls the continuation and stop of the filter coefficient update according to the reception C / N. As an example of the filter coefficient update control information, “received C / N exceeds a threshold set by the C / N evaluation unit 52 (here, AdB) and the input symbol of the receiving side adaptive equalizer 51 is a predetermined value. If the number of symbols (here, B symbols) is exceeded, the filter coefficient is fixed.

  Subsequently, in step S <b> 5, the reception apparatus 20 performs adaptive equalization processing on the reception signal by the reception side adaptive equalizer 51, and the reception C / N equivalent value obtained from the reception side filter coefficient update control unit 53. The filter coefficient on the receiving side is fixed using the filter coefficient update control information based on. After the reception-side filter coefficients are fixed, the reception-side adaptive equalizer 51 operates as a general fixed filter coefficient equalizer with respect to the input received signal with the filter coefficients fixed. At the same time, the reception-side filter coefficient is output to the reception-side filter coefficient update control unit 53. Here, when the receiving side adaptive equalizer 51 satisfies the control information and reaches a stable operation on the receiving side, the receiving side adaptive equalizer 51 operates so as to bring the distorted signal closer to an ideal signal. As a result, the inverse characteristic of the impulse response of the transmission path can be obtained from the filter coefficient of the receiving side adaptive equalizer 51. Therefore, it is desirable to perform under the high reception C / N when performing the equalization operation repeatedly between transmission and reception as the initial operation mode on condition that the reception-side adaptive equalizer 51 operates stably. For example, as an example under a high reception C / N, when a satellite transmission path is assumed, it may be possible to use a large reception antenna in fine weather. More preferably, a large parabolic antenna of several meters used in a satellite earth station or the like may be used.

  Subsequently, in step S <b> 6, the reception device 20 outputs the reception-side filter coefficient obtained by the filter coefficient update control unit 53 to the transmission-side filter coefficient update unit 12 in order to set the transmission-side adaptive equalizer 13. . At the same time, the transmission side filter coefficient update control unit 12 increments the transmission / reception equalization repetition number P by one.

  Subsequently, in step S7, the transmission apparatus 10 proceeds to step S8 when the repetition number P of equalization operations between transmission and reception is equal to or less than the target number G under the control of the transmission-side filter coefficient update control unit 12. The filter coefficient of the side adaptive equalizer 13 is updated. Here, it is not always necessary to make the information of the same filter length between transmission and reception, but it is preferable to keep the filter length of the adaptive equalizer between transmission and reception at the same length. Can be applied to the transmission-side filter coefficients as they are. If the number of repetitions P is less than or equal to the target number G, it means that the initial operation mode is continued, and the transmission side adaptive equalizer 13 fixes the filter coefficient with the value of the reception filter coefficient obtained in step S6. Thus, the transmission of the modulated wave signal is continued, and the filter coefficient update operation performed in the original adaptive equalization processing is not performed. That is, when a decision feedback type adaptive equalizer as shown in FIG. 4 is considered, the transmission side adaptive equalizer 13 operates as a decision filter type decision feedback equalizer with respect to the input transmission signal. .

  Through the processing in step S8, the transmission apparatus 10 transmits the transmission signal that is equalized from the transmission-side adaptive equalizer 13 using the reception-side filter coefficient, in which the reverse characteristic of the transmission line is reflected before passing through the transmission line. Signal. Therefore, when a transmission signal that reflects the reverse characteristics of this transmission path passes through the same transmission path, the received signal is a signal with a reduced influence of distortion because the effect is to cancel the transmission path distortion. It becomes.

  Therefore, when a transmission signal that reflects the reverse characteristics of this transmission path passes through the same transmission path, the received signal is a signal with a reduced influence of distortion because the effect is to cancel the transmission path distortion. It becomes.

  If the transmission / reception equalization repetition number P exceeds the target number G in step S7, the process does not proceed to step S8, which is the filter coefficient update process of the transmission side adaptive equalizer 13, and the current filter coefficient is continuously used. To do. That is, returning to step S3, the transmission side adaptive equalizer 12 operates with the filter coefficient stored in the transmission adaptive equalizer 13, and shifts to the steady operation mode.

  Further, by repeating Step S3 to Step S8 between the transmitter and the receiver, a more accurate filter coefficient is supplied from the receiver 20 to the transmitter 10, and the transmission signal in which the reverse characteristic of the transmission path is reflected in advance in the transmission signal Can be generated.

  FIGS. 7A to 7F show changes in the constellation of 32APSK when the calculation flow of FIG. 6 is performed once (transmission / reception equalization repetition number P = 1). Here, a satellite transmission path was assumed as the transmission path system used in the computer simulation. That is, the IMUX filter, TWTA, and OMUX filters that constitute a general satellite repeater are assumed as the satellite transmission path, and the system is reproduced by computer simulation. The operating point of TWTA was calculated for 3.4 dB. In the transmission side and reception side adaptive equalizers, step size: 2E-4, feed forward filter tap length: 10, and feedback filter tap length: 14 were used. The receiving-side adaptive equalizer 53 is operated as the above-described blind equalizer, and the adaptive algorithm uses the LMS algorithm and the blind algorithm uses the GCMCA algorithm.

  FIG. 7A shows the constellation of the 32APSK transmission signal when P = 0 in step S2. At this time, since the transmission side adaptive equalizer is not operating, a normal ideal transmission signal is transmitted. Next, FIG. 7B is a 32APSK reception signal at P = 0 in step S4. From FIG. 7B, it can be seen that the transmission signal is deteriorated due to transmission path distortion generated in the satellite repeater. FIG. 7C shows a constellation of received signals corresponding to the received C / N = 30 dB at P = 0 in step S5. FIG. 7D shows a constellation obtained by performing reception-side adaptation processing on the reception signal corresponding to reception C / N = 30 dB shown in FIG. 7C when P = 0 in step S5. It can be seen that the quality of the constellation is improved by the adaptive equalization processing.

  FIG. 7E shows a constellation of a transmission signal obtained by performing transmission-side adaptive equalization processing on the transmission signal using the reception-side filter coefficient at P = 1 in step S3. Since the constellation in FIG. 7 (e) reflects the reverse characteristics of the transmission path with respect to the ideal transmission signal that has not been subjected to the transmission equalization processing shown in FIG. 7 (a), the constellation has a reverse distortion. You can see that it is spreading. Next, FIG. 7 (f) shows the constellation of the received signal after P = 1 in step S4, that is, the transmission signal reflecting the transmission path characteristics shown in FIG. 7 (e) passes through the transmission path. Comparing FIG. 7 (f) and FIG. 7 (b), the constellation of FIG. 7 (f) shows that the transmission signals subjected to the inverse distortion characteristics in advance in FIG. Since the characteristics are canceled out, it can be seen that the signal quality is improved as compared with the received signal constellation of FIG.

  Next, FIG. 8 shows an example of a computer simulation result of 32APSK coding rate 4/5 C / N versus bit error rate characteristics in the signal of FIG. 7 (f) obtained by the flow of FIG. Since the signal of FIG. 7 (f) is a reception result of signals transmitted all at once, the adaptive equalizer is applied to the receiver when the signal of FIG. 7 (f) is adaptively equalized on the receiving side (case A). The calculation was performed for the case where there was no (case B). FIG. 8 shows a characteristic (case C) when the signal of FIG. 7B is decoded without using an adaptive equalizer, and only the reception-side adaptive equalizer 53 is used for the signal of FIG. 7B. The characteristics (case D) in the case of decoding are also shown. For use in calculating the likelihood table of pilot signals as shown in FIG. 13 at the time of LDPC decoding, only the symbols belonging to the outermost circle are used for the cases A, B, and D, the inner circle and A pilot signal was used for symbols belonging to the innermost circle. For case C, pilot signals were used for all symbols.

  Referring to FIG. 8, the configuration according to the present invention is used ((Case A), (Case D) rather than the transmission performance (Case D) where the equalizer is not used (Case C) or normal blind equalization). It can be seen that the transmission performance is improved in both cases B)). In addition, the transmission performance of case A is further improved than that of case B, indicating that the transmission performance can be improved by further equalizing the signal (FIG. 7 (f)) reflecting the transmission path distortion. Yes.

  As a feature of this method, when a satellite transmission path is assumed, it is possible to transmit transmission signals having the performance shown in Case B of FIG. 8 all at once, and to receivers not equipped with other equalizers. In contrast, similar performance can be obtained. In addition, in this embodiment, the effect when the filter coefficient update from the receiving apparatus 20 to the transmitting apparatus 10 is performed once is clarified. However, the above processing is performed by repeatedly updating the filter coefficient between the transmitter and the receiver. The accuracy can be increased, and further improvement in transmission performance can be obtained. Further, the present system is not limited to 32APSK, and it is possible to improve transmission characteristics for signals including transmission path distortion when using various modulation systems having a plurality of amplitude levels. Further, the transmission device 10 and the reception device 20 can be configured to execute the initial operation mode periodically or at any timing for monitoring the received C / N equivalent value and updating the filter coefficient. . In addition, when it is desired to configure the reception device 20 so as to identify whether the reception device 20 is in the initial operation mode or the steady operation mode, the transmission device 10 uses a flag for identifying the mode of the reception device 20. May be included in the transmission control signal (TMCC or the like).

  In the above-described embodiment, the case where a specific satellite repeater, a modulation scheme, and an LDPC code are applied has been described. However, the present invention is not limited to a terrestrial repeater, another modulation scheme, and an arbitrary likelihood calculation. It is clear from the description of the embodiments that the present invention can be applied to error correction codes. Further, the present invention is not limited to the advanced BS modulation signal system, and can be applied to any digital transmission to which the present invention can be applied. Accordingly, the invention should not be construed as limited by the embodiments described above, but only by the claims.

  Since the present invention can suitably reduce transmission path distortion on the receiving side, it is useful for a transmission device and a reception device of any digital transmission method.

DESCRIPTION OF SYMBOLS 10 Transmission apparatus 11 Advanced BS modulation signal generation part 12 Transmission side filter coefficient update control part 13 Transmission side adaptive equalizer 20 Reception apparatus 51 Reception side adaptive equalizer 52 Reception C / N determination part 53 Reception side filter coefficient update control part DESCRIPTION OF SYMBOLS 100 Transmission apparatus 110 Frame generation part 120 LDPC encoding part 130 Energy spreading | diffusion part 140 Mapping part 150 Time division multiplexing / orthogonal modulation part 200,200-1,200-2, ..., 200-N receiving apparatus 210 Channel selection part 220 Quadrature detection unit 230 Transmission control signal decoding unit 240 Energy despreading unit 250 LDPC decoding unit 251 LDPC decoder 252 Pilot signal extraction unit 253 Pilot signal averaging processing unit 254 Likelihood table generation unit 255 Likelihood table 256 Decision feedback FIR Filter 300 Satellite repeater 2 61 feed forward filter (FF)
2562 Equalizer Output Unit 2563 Determination Unit 2564 Feedback Filter (FB)
2565 Adder 2566 Filter coefficient updater

Claims (11)

In digital transmission in which a plurality of receiving apparatuses receive a signal transmitted from one transmitting apparatus via a transmission path having common transmission path characteristics, the digital transmission transmission signal is adaptively equalized based on a complex error amount, A transmission device that transmits a modulated wave signal including the reverse characteristic of the transmission path ,
When transmitting a modulated wave signal, an initial operation mode for determining a filter coefficient necessary for setting the adaptive equalization of the main signal, and a steady operation mode for transmitting a modulated wave signal in a steady state after determining the filter coefficient Have
Modulation signal generating means for generating a modulated wave signal of the main signal;
Transmission-side adaptive equalization means for performing adaptive equalization on the generated modulated wave signal of the main signal;
Receiving a filter coefficient of adaptive equalization generated by adaptive equalization of the main signal based on a complex error amount from a specific receiver among the plurality of receivers in an environment with good signal quality; The filter coefficient setting of the transmission side adaptive equalization means is controlled so that the transmission signal subjected to adaptive equalization processing becomes a transmission signal reflecting the reverse characteristic of the transmission line before passing through the transmission line. A transmission side filter coefficient update control means,
The transmitting filter coefficient update control means, in said initial operating mode until it receives a filter coefficient generated by the specific receiving device outputs a modulated wave signal output from said modulation signal generating means to the outside In this way, the adaptive equalization of the transmission-side adaptive equalization means is controlled by the filter coefficient finally determined for the filter coefficient generated on the reception side in the steady operation mode. A filter apparatus for setting a filter coefficient of   The filter coefficient set for adaptive equalization by the transmission-side adaptive equalization means has the same filter length as the filter coefficient used for adaptive equalization on the reception side. Transmitter device.   The transmission-side filter coefficient update control unit repeats reception of the reception-side filter coefficient a plurality of times in the initial operation mode, and finally determines a filter determined by whether or not the number of repetitions exceeds a preset value. The transmission apparatus according to claim 2, wherein the transmission apparatus is determined as a coefficient.   4. The filter coefficient according to claim 1, wherein the filter coefficient is a value determined under a situation where a reception C / N equivalent value defined on a reception side is equal to or greater than a predetermined threshold value. 5. Transmitter device.   The transmission apparatus according to any one of claims 1 to 4, wherein the transmission side adaptive equalization means is a feedback type adaptive equalizer used in combination with an LDPC code. In digital transmission in which a plurality of receivers receive a signal transmitted from one transmitter via a transmission line having common transmission path characteristics, the digital transmission signal is adaptively equalized based on a complex error amount to generate a modulated wave. A specific receiving device for transmitting signals,
When transmitting a modulated wave signal, an initial operation mode for determining a filter coefficient necessary for setting the adaptive equalization of the main signal, and a steady operation mode for transmitting a modulated wave signal in a steady state after determining the filter coefficient Have
Quadrature detection means for quadrature detection of a modulated wave signal of digital transmission;
A reception C / N determination unit that determines a reception C / N with respect to a quadrature-detected main signal and generates a reception C / N equivalent value;
Receiving-side adaptive equalization means that operates in an environment with good signal quality and performs adaptive equalization based on a complex error amount with respect to a quadrature-detected main signal;
A reception side that generates a filter coefficient update control signal that controls continuation and stop of filter coefficient update using the received C / N equivalent value, and controls setting of filter coefficients for adaptive equalization of the reception side adaptive equalization means Filter coefficient update control means,
At the initial operation mode, the reception side filter coefficient update control means have a means for transmitting the filter coefficients set in the adaptive equalization of the reception side adaptive equalization means to the transmitting side,
In the steady operation mode, the receiving apparatus receives a transmission signal that is subjected to adaptive equalization processing on the transmission side and reflects the reverse characteristic of the transmission path before passing through the transmission path .   The filter coefficient set for adaptive equalization of the reception-side adaptive equalization means has the same filter length as the filter coefficient used for adaptive equalization on the transmission side. Receiver device.   The reception-side filter coefficient update control means repeats transmission to the transmission side of the filter coefficient set to the adaptive equalization of the reception-side adaptive equalization means a plurality of times in the initial operation mode. The receiving device according to claim 7.   The reception-side filter coefficient update control means is a control for determining the filter coefficient so that the filter coefficient of the reception-side adaptive filter that operates under the condition where the specified reception C / N equivalent value is equal to or greater than a predetermined threshold value can be output. 9. The receiving apparatus according to claim 6, wherein a signal is sent to the receiving side adaptive equalization means.   The receiving apparatus according to any one of claims 6 to 9, wherein the receiving side adaptive equalization means is a feedback type adaptive equalizer used in combination with an LDPC code.   A transmission / reception apparatus comprising: the transmission apparatus according to claim 1; and the reception apparatus according to claim 6.

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